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The value of the other complex fertilisers enumerated on p. 136, depends
essentially on their nitrogen content, the proportions of phosphoric anhy-
dride and potash being rarely required.

Their analysis includes the following :

1.  Moisture.—See General Methods, 2.

2.  Nitrogen.—The total nitrogen (organic) is estimated by the Ulsch-
Kjeldahl method (see General Methods, 3, C).   With voluminous and non-
homogeneous substances (hair, horn, nails, and the like), it is well to heat
50 or 100 grams in a dish on a water bath with 100 or 200 c.c. cone, sulphuric
acid or phosphosulphuric acid, the mixture being occasionally shaken, until
a homogeneous paste is obtained.   This is made up to a definite volume
with cone, sulphuric acid and an aliquot part corresponding with 1-5 grams
of the original substance, according to the presumed richness in nitrogen,
treated in the ordinary way.

3.  Phosphoric  Acid,   Potash.—10-20 grams of the  substance are
charred as indicated in note i on p. 124, the phosphoric acid and the potash
being then estimated in the well carbonised product as described in General
Methods, 4 and 5.

* *

Guanos may contain, according to their origin : nitrogen, 1-19 ; P2O5;
1-40; and K2O, 0-5-9%. Peruvian guano contains, on the average: N, 7,
P2O5, 14 ; and K2O, 2%. Italian bat guano (Sardinia) contains about 4% N, 5%
P2O6, and i% K2O.

In oil seed cake (arachis, cameline, colza, cotton seed, linseed, sesame, etc.)
may be found : 2-7% N, 0-5-3% ^sPs. and 0-2-2% K2O.

In peat: 0-3-3% N, 0-1-0-8% P2OS, and 0-1-2% K2O.

Various other organic residues contain about 7-15% N, 0-5-2% P2O5, and
°'3~I'5% KaO- Exhausted meat residues from meat-extract factories contain
4-11% N, 10-25% P2O6, and about 0-5% K2O.quently made up to volume and the nitrogen in an aliquot part of the